Treatment of filaments to improve strength in tension



March 31, 1959 J. A. cuuLo 2,880,057

TREATMENT OF FILAMENTS TO IMPROVE STRENGTH IN TENSION Filed Jan. 22, 1958 INVENTOR JOHN A. CUCULO ATTORNEY United States Patent TREATMENT OF FILAMENTS TMPROVE STRENGTH IN TENSION John Anthony Cuculo, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a. corporation of Delaware Application January22, 1958, Serial No. 710,475

13 Claims. (Cl. 18-54) cold drawing is facilitated by heating the yarn during the drawing step. The heating operation may be carried out by inserting a hot pin, a hot plate, or hot fluid bath between the feed roll and draw rolls of the drawing apparatus or by using a heated feed roll. perature limitations were recognized by Leben and Little (British Patent 603,840, issued June 23, 1948), who taught that difficulties in applying heat and tension simultaneously are aggravated as the melt temperature of the filaments is approached and it is, therefore, preferred that the drawing should take place at a yarn temperature considerably less than the melting temperature and preferably below the range of maximum crystallization rate as defined by W. H. Cobbs, Jr., et al. J. Polymer Sci. 10, 3, 283 (1953). It is also taught that if undrawn yarn is heated without applying drawing tension the yarn becomes brittle and subsequently can be drawn only with great difiiculty.

Embrittlement of polyester filaments is correlated with resin crystallization and has long beenrecognized as a dominant influence upon the properties of these and the majority of polymers. Increased crystallization has heretofore been considered generally undesirable because of its effect on reducing drawability and toughness of undrawn filaments. W. H. Cobbs, Jr., et al. ibid, 275-290, considered, by using the technique of infra-red absorption, the increase in crystallinity with the increase in density of such polymers. The invention herein described and claimed departs from the accepted conclusions derived from these teachings of the art and in contradistinction thereto, provides a process for making more crystalline, in the undrawn state, polymers from which superior products can be produced.

The primary object of this invention is to provide an improved and economical method for manufacturing products of synthetic linear polyesters, polyamides and like synthetic linear polymers. Another object is to provide a method of attaining higher draw ratios of said polymers and concurrently superior physical properties. Yet another object is to provide a method of increasing the crystallinity of linear polymers and thereafter drawing the polymers to produce a filament of remarkably high tensile strength. A further object is to provide a process of drawing highly crystalline polymer filaments at high draw ratios. These and other objects of the invention will hereinafter appear.

Drawing tern! 2,880,057 Patented Mar. 31, 1959 These objects are accomplished in accord with the iri= vention by a process in which orientable and crystalliz able polymers are extruded into elongated shapes, such as films, filaments, yarns, ribbons and the like; the extruded shape, in the undrawn state, is heated at a temperature in the range of the maximum crystallization rate for the particular polymer and, while under zero tension, is held at said temperature until the crystallinity is incrementally increased, in accordance with the polymer treated, from 10% up to as much as 70%.

In one embodiment of the invention normally polymerized polyethylene terephthalate in granular form is heated in an atmosphere of dry nitrogen in accord with the process described in the P. J. Flory US. Patent 2,172,374, issued September 12, 1939, or by any other suitable process, to increase its inherent viscosity to about 1.0. The resulting polymer is melt extruded in any suitable extruder to a 20 ml. diameter filament and the filament quenched in water at room temperature in an undrawn state. The filament is then heated under zero tension, to a temperature between 173 and 175 C. in air, a suitable liquid bath, such as oil, or in contact with a heated roller, for about 10 seconds, and thereafter, at that temperature, the filament is drawn 6.0/1 (ratio=final length/original length) to produce a filament having a tensile strength of 7.1 (125,000 p.s.i.) to 7.2 g.p.d. (grams ,per denier) and remarkable stiffness.

In one example of the above embodiment, the polymer, prior to treatment, had a crystallinity of essentially zero as extruded and undrawn and, after the heat treatment of the filament by the process of this invention, it at tained a crystallinity of about 10%. Finally, after complete processing, which involved drawing and heat setting, the crystallinity rose to 48%. The superior processability and physical properties of the filament were attained,it is believed, primarily because of the increased crystal-' linity with its accompanying morphological modifications, which the heat treatment, prior to drawing, induced. Moreover, without treatment by the process of the invention, solid state polymerized polyethylene terephthaice '- late, with inherent viscosities above about 0.90, could not polymers, since the higher molecular weight slows the terephthalic cyclohexane; the polyamides, e.g., the diamine dicar-' be cold drawn without breaking to a ratio of 4/ 1.

The heat treatment of the undrawn, extruded filament induces crystallinity which is possibly accompanied by a change in crystalline morphology. As a consequence, the process is most useful with higher molecular weight of such resins include synthetic linear polyesters, e.g.,-

polyethylene terephthalate and the polyester derived from acid and trans-bis-1,4-(hydroxyrnethyl) boxylic acid polymers, e.g., 66, 610 polymers; the amino acid polymers, e.g., the 6 polymers and copolymers there of, e.g., 6/ 66; 6/610/ 66; 66/610 etc.; and the crystalline polyethylene, e.g., linear polyethylenes with densities be tween .95 and .98 and their crystalline copolymers.

The process of the invention, with the aforesaid highly crystallizable polymers, gives results ranging from (1) excellent improvement in processing and the resultant physical properties of the extruded product, e.g., a filament of polyethylene terephthalate with an inherent viscosity above 0.75 and preferably above 0.85, permits the attainment'of 'high'draw ratios and markedly improved products to (2) less dramatic but, nevertheless, general upgrading of such polymers as high density linear polyproducts not so treated. The table identifies the polymers of each example; gives their inherent viscosities, the temperature and time of heat treatment, the draw ratio, the temperature and time of heat setting (more ethylene, density t 610 (P Y Y fully described below); the mandrel bend; the fatigue resebacarnide'), inherent 'viscosity of about 1.2 and prefsistance; and the tensile strength and percent elongation. erably 1.3; and such polyamides as 6 (the polymeric The mandrel bend recovery is measured in this mancaprolactam) inherent'viscosity above 1.2; 66 (polynerz. a filament is wrapped to 20 times around a 90 hexamethylene adipamide), inherent viscosity above 1.5; mil mandrel and left on the mandrel for 4 minutes. At and the copolymers, e.g., 66/610, 6/66/610, with in- 10 the end of this time the filament is removed from the herent viscosities above about 1.2, etc. mandrel and placed in water at 23 C. for one hour,

The attached drawing illustrates diagrammatically then removed .and the number of loops remaining is apparatus in which the process of the invention can be counted. The mandrel bend recovery, in percent, equals carried out. In the figure, 1 represents an extruder, 2 I a quench tank; and 3 a heating chamber. The drawing No. of loops remaining rolls are (slow rolls) 4 and (fast rolls) 6, with.5 the No. of original loops drawing medium tank and 7 the wind-up roll.

The polymer, after. treatment to increase its molecular Fatigue reslstance is determined on a rectangular tuft weight (solution viscosity), is charged into the extruder of bristles x A". This tuft 1s mounted in a plate 1, maintained at a temperature above the melt tempera- 7 "'thick with a /1" length of the tuft extended above ture or the polymer, of the well known type provided the plate. The tuft is struck laterally by a diameter with a die 8 to produce a continuously extruded product pin fastened to the periphery of a wheel having a 1 such as a filament X. The filament X in the undrawn radius. The wheel is rotated at 1725 r.p.m. and the state. is passed into a quench tank 2 containing water pin strikes the tuft at a point A" above the face of the or. other inert liquid, at room temperature, and still in plate. The fatigue resistance, in percent, equals 100 an undrawn state (i.e., the polymer isunoriented), the times the number of unharmed bristles divided by the filament is passed into .heater 3, which may be an oil total. number of bristles. The tensile strength and perbath or a fluid heating bath, and therein thefilament is cent elongation is measured on an Instron Universal heated 'at zero'.tension for a suflicient time and at a Tensile Tester by standard methods.

Table' Heat Setting Mandrel Fat Tensile t Inherent Caliper Process Heat 1 Bend Res Str./Elong. Example Polymer Viscosity (mils) Temp. Treatment Draw Ratio Reeov. (per- (p.s.i.

C.) Time Temp. Time (percent) cent) X10 (min.) 1 C.) (min.) percent) 0.982 '18 None None 3. 2/1-s 190 4.5 .65 .80 3. 75/25 0. 98: 18 None None 3.2/1-sR 190 4. 0 66 92 3. 70/25 0.97: 18 None None 3.25/1-D 190 3.7 67 91 3.95/61 0. 97: 18 None None 3 25/1-DR 190 3. 4 66 89 3. 80/50 0. 97: 18 None None 4. 0/1-D 190 4. 5 65 75 4. 60/31 0. 942 18-20 None None 3. 0/1-S 190 1. 5 70 91 3. 80/33 0.57: 18-20 None None 4.8/1-S 190 2.0 79 7 7. 60/51 0. 892: 20 17 0. 18 6.0/1 190 3. 0 70 91 9. 10/25 0. 90: 18-20 173-175 0.18 6.0/1 190 15.0 44 100 12. 50/-- 0. 891 20 17 0. 26 6. 0111 190 3. 0 68 91 9. 70/23 0.942 19 20 0.67 5.4/1 190 15.0 49 99 9 80/125 0. 942: 19 196-197 0. 22-044 6.0/1 None None 10. 90/ 1.36 25-26 0.69 6.0/1 170 1.5 90 100 9.10/1s.7 1.36;; 25-26 None None 6. 0/1 170 1. 5 88 100 7. /18. 7 1. 72-1. 791 21-22 216-217 0.21 4.0/1 170 3.0 86 98 6. 92/13 1.051] 21-22 220-222 0.19 4.0/1 170 3.0 90 99 6. 74/19.8 1. 651/ 21-22 None None 4.0/1 170 3.0 89 95 6. 24/24.0 1.7611 25 187-189 0.68 3.6/1 170 3.0 95 100 6.47/19 1. 761 25 None None 3. 6/1 170 3. 0 94 100 5. /10

Viscosity of undrawn filament. Oallper in mils of undrawn filament.

1 yalnherent viscosity .5% by weight in M-eresol.

' I=Inherent viscosity .5% by weight in tetra-ehloroethane and phenol 40/60..

suitable temperaturefor'elfecting the crystallization herein described. The thus'treatedfilament is thereafter passed over slowdrawrolls 4 operated at an rpm. such that the filament issubjected to substantially no stretching between the exit of heater 3 and roll 4. From roll 4the filamentis fed-through the drawing medium tank set, 1 at the prescribed temperature, to power operated rolls 6, the rpm. of which draws the filament passing between the rolls to the desired ratio of drawn length to undrawn: length. The -drawing medium in tank 5 may be a'ny suitable fluid such as a petroleum oil, a silicon oilnorithelike, maintained at, above, or below the temperature in chamber 3. The thus treated filament is then wound-up on roll 7. Sutficient wraps of the filaments around the rollsare made to insure no slippage, usually 2 or 3 wraps around rolls 4 and 6 are adequate for this purpose.

' In the table-which follows, products are described which have been treatedin accord with the process of the :inventionand comparisons made, in some cases, with In*the-table,"Emaples 1-a to 1 show polyethylene terephthalates, which have not been treated by the process of the invention, having high viscosities and low tensile strength filaments with good fatigue resistance. Example 1-g, a low viscosity polymer, shows poor fatigue resistance but fairly good tensile strength, in contrast to the aforementioned polymers. Examples 2-6 show the unexpected eifect of the invention which results in superior tensile strength and excellent fatigue resistance. Examples' l-a to 1 illustrate filaments having minimum draw'ratios and Examples 2-6 show the highdraw'ratios and stiffness. The superiority of the products subjected to the process of the invention is also apparent from a comparison of Examples 7, 9-10 and 12, respectively, with Examples 8, '11, and 13.

Syntheticresin crystallinity is, it has been found, increased by heating the undrawn resin for a specified period of time at a temperature peculiar to the particular resin: "The'optimum temperature and time-of heat treatment can'be readily determined by infra-red examination by the W. H. Cobbs, Jr., et a1. technique, ibid., or by any other suitable method. The temperature of treatment for optimum crystal growth for the described crystalliz able resins has been found to be generally about 5075 C. below the melting point of the resin and is continued generally for about seconds to about 1 minute at temperature.

Heat setting, described in the table, involves subjecting a drawn filament to a prescribed temperature, in any medium desired (air, water, oil) for a specific period of time and under a desired tension. This heat setting is a well known, accepted practice in the filament and yarn technology. It can be carried out continuously or in batch process.

The extruded and drawn products of the invention are useful for many purposes, for example, filaments of the polymers are useful in the preparation of yarns, tire cord, in the weaving of cloth, rope and in like textile uses, in the preparation of filter cloth, and in other uses which require toughness and exceptional strength.

I claim:

1. In a process of increasing the crystallinity and attainable draw ratio and improving the physical properties of orientable, crystallizable, synthetic linear polymers, the steps which comprise extruding a melt of an orientable, crystallizable, synthetic linear polymer into an elongated shape, heating the shape, in an undrawn state and under substantially zero tension, to a temperature within the range of substantially maximum crystallization rate and for a time that will produce substantial crystal growth and thereafter cold drawing the resulting shape.

2. The process of claim 1 in which the polymer has a molecular weight corresponding to that of a solid phase polymerized polymer.

3. The process of claim 2 in which the shape is heated to a temperature between 160 and 210 C. for from 5 to about 60 seconds.

4. The process of claim 1 in which the shape is a filament.

5. A polyethylene terephthalate filament having a draw ratio of at least 5.0/ 1, the polymer content of which has an inherent viscosity above 0.75.

6. In a process of increasing the crystallinity and attainable draw ratio and improving the physical properties of polyethylene terephthalate, the steps which comprise extruding a melt of polyethylene terephthalate into an elongated shape, heating the shape, in an undrawn state and under substantially zero tension, to a temperature within the range of substantially maximum crystallization rate and for a time that will produce substantial crystal growth and thereafter cold drawing the resulting shape.

7. In a process of increasing the crystallinity and attainable draw ratio of polyethylene terephthalate, the steps which comprise melting polyethylene terephthalate having an inherent viscosity above 0.89, as determined in a solution of tetrachloroethane and phenol, 40/60, containing 0.5% by Weight of the polyethylene terephthalate; extruding the melt into an elongated shape; heating the shape in an undrawn state and under substantially zero tension to a temperature between 160 and 210 C. for from 5 to about seconds; and thereafter cold drawing the resulting shape.

8. The process of claim 1 in which the polymer is polyhexamethylene adipamide.

9. The process of claim 1 in which the polymer is polymeric caprolactam.

10. The process of claim 1 in which the polymer is polyhexamethylene sebacamide.

11. The process of claim 1 in which the polymer is linear polyethylene.

12. A polyethylene terephthalate filament having a draw ratio of about 6.0/1 and an inherent viscosity of from 0.89 to 0.97 as determined in a solution of tetrachloroethane and phenol, 40/60, containing 0.5% by weight of the polyethylene terephthalate.

13. A polyethylene terephthalate film having a draw ratio of at least 5.0/1, the polymer content of which has an inherent viscosity above 0.75.

Pace June 12, 1951 Pace Dec. 18, 1951 

1. IN A PROCESS OF INCREASING THE CRYSTALLINITY AND ATTAINABLE DRAW RATIO AND IMPROVING THE PHYSICAL PROPERTIES OF ORIENTABLE, CRYSTALLIZABLE, SYNTHETIC LINEAR POLYMRS, THE STEPS WHICH COMPRISE EXTRUDING A MELT OF AN ORIENTABLE, CRYSTALLIZABLE, SYNTHETIC LINEAR POLYMER INTO AN ELONGATED SHAPE, HEATING THE SHAPE, IN AN UNDRAWN STATE AND UNDER SUBSTANTIALLY ZERO TENSION, TO A TEMPERATURE WITHIN THE RANGE OF SUBSTANTIALLY MAXIMUM CRYSTALLIZATION RATE AND FOR A TIME THAT WILL PRODUCE SUBSTANTIAL CRYSTAL GROWTH AND THEREAFTER COLD DRAWING THE RESULTING SHAPE. 